Observed Changes in Temperature Extremes over Greece: Warm and Cold Spells

The daily maximum and minimum temperatures measured by the HNMS’s stations from 1960 to 2022, are used to compute percentile-based indices capturing the percentage of days below or above the 10th and 90th percentile, respectively (TN10p, TX10p, TN90p, TX90p), and event duration indicators (WSDI and CSDI). The climate extremes indices are evaluated assuming two different reference periods (1961–1990 and 1991–2020), and trend analysis is performed using the Mann–Kendall test. The results show a significant increase in the frequency of the warm days and nights. The magnitude and perceived timing of trends depend on the baseline chosen. Using the warmer 1991–2020 reference period dampens the upward trends in warm–extreme indices and amplifies the downward trends in cold extremes.